Electron beam columns are well known for use in electron microscopy for imaging surfaces and thin samples and for electron beam lithography, such as for imaging a pattern onto a substrate. Conventional electron beam columns for electron microscopy and lithography are typically used to produce a scanning probe or to illuminate a sample or an aperture using a series of electron beam lenses, including magnetic or electrostatic lenses.
A well-known variant, the microcolumn, is a very short and small diameter electron beam column, often used in an array of such columns. Microcolumns are structures including microlenses and deflectors. In general, the microlenses are multiple layers of silicon chips or silicon membranes spaced apart by insulating layers and having bore diameters that vary from a few to several hundred μm. Such microlenses may include a plurality of microlens components or elements, accurately aligned for the purpose of focusing electron beams. Electrodes of the microlenses may include silicon membranes formed from a polished wafer containing a plurality of die, wherein a membrane may be formed at the center of each die, possibly by wet isotropic etching.
Coupling the insulating and microlens silicon layers of the microcolumn is typically achieved by anodic bonding. However, anodic bonding must be conducted at elevated temperatures, which typically requires several hours of heat-up (to approximately 400° C.) and cool-down time, as well as a physical connection of a high voltage probe, during which time drift, bond-induced shift, and expansion can degrade the alignment. This process must then be repeated for each additional layer. Because the apertures in the microlenses must be precisely aligned, assembly of the microcolumn is complex and time-consuming. For example, one assembly method requires each lens to be aligned under an optical microscope and anodically bonded one at a time. In addition, sodium ion migration from insulating layers to conductive layers during operation at elevated voltages can cause arcing and, consequently, failure of the microcolumn.